Glyphosate and Urea Co-Exposure: Impacts on Soil Nitrogen Cycling

Glyphosate, the most widely utilized herbicide, frequently coexists with nitrogen fertilizers such as urea in soil environments. This study investigates the effects of combined glyphosate and urea exposure on a soil system over 98 days. The research reveals that co-exposure increases glyphosate and AMPA residues while altering soil nutrient levels. It enhances nitrate and nitrite reductase activities but inhibits urease, leading to decreased bacterial diversity and altered nitrogen cycling functions. Gene expression analysis showed downregulation of nirK and upregulation of amoA and napA, disrupting nitrate and ammonium storage and reducing plant-available nitrogen. A Partial Least Squares Structural Equation Modeling (PLS-SEM) analysis demonstrated that co-exposure indirectly decreased soil total nitrogen, NH4+-N, and NO3--N contents by modulating enzyme activities. These results suggest that co-exposure to glyphosate and urea disrupts soil nitrogen cycling, potentially impacting on agricultural productivity. The study highlights the complex interactions between herbicides and fertilizers in soil environments and underscores the need for further research to understand the implications for wider soil health and crop production in agriculture systems.